The present disclosure relates generally to optical communication and array-type light-emitting devices.
Light emitting diodes (LEDs) are an important class of solid-state devices that convert electric energy to light. They generally comprise an active layer of semiconductor material sandwiched between two oppositely-doped cladding layers. When a bias is applied across the cladding layers, electrons and holes are injected into the active layer where electrons and holes recombine to generate photons, or light. Recent advances in LEDs have resulted in highly efficient light sources that surpass the efficiency of filament-based light sources, providing light with equal or greater brightness in relation to input power.
Disadvantage of conventional LEDs used for lighting applications is that they cannot generate white light directly from their active layers. Recently, two different ways have been introduced to produce white light from conventional LEDs. One way to produce white light from conventional LEDs is to combine different wavelength of light from different LEDs. For example, white light can be produced by combining the light from red, green and blue LEDs or combining the light from blue and yellow LEDs. The other way to produce white light is using yellow phosphor, polymer or dye to downconvert portion of the light from a blue LED into yellow light. A white LED is seemly produced because it simultaneously emits both blue and yellow light, which combine to provide white light.
Since white LEDs are developed, LEDs have widely used because of their high durability, longevity, portability, low power consumption, absence of harmful substances such as mercury, and so forth. Often-seen applications of LEDs include white light illumination, indicator lights, vehicle signal and illuminating light, LCD backlight modules, projector light sources, outdoor displays, and so forth. Nevertheless, other applications might use LEDs to replace their light sources.